Blocking swelling-activated chloride current inhibits mouse liver cell proliferation.

A non-transformed mouse liver cell line (AML12) was used to show that blocking swelling-activated membrane Cl- current inhibits hepatocyte proliferation. Two morphologically distinguishable cell populations exhibited distinctly different responses to hypotonic stress. Hypotonic stress (from 280 to 221 mosmol kg(-1)) to rounded, dividing cells activated an ATP-dependent, outwardly rectifying, whole-cell Cl- current, which took 10 min to reach maximum conductance. A similar anionic current was present spontaneously in 20 % of the dividing cells. Hypotonic stress to flattened, non-dividing cells activated no additional current. The Eisenman halide permeability sequence of swelling-activated anionic current in the dividing cells was SCN(-) > I(-) > Br(-) > Cl(-) > gluconate. Addition of either 4,4'-diisothiocyanatostilbene-2,2'-disulfonate (DIDS), 5-nitro-2-(3-phenylpropylamino) benzoic acid (NPPB), tamoxifen or mibefradil inhibited swelling-activated anionic current. Hyperosmolarity by added sucrose inhibited the spontaneous anionic current in dividing cells. Added Cl- channel blockers NPPB (IC50 = 40 microM), DIDS (IC50 = 31 microM), tamoxifen (IC50 = 1.3 microM) and mibefradil (IC50 = 7 microM) inhibited proliferative growth of AML12 as determined by cell counts over 4 days or by protein accumulation over 2 days. Only the inhibitory effects of NPPB and mibefradil reversed with the drug washout. Hyperosmolarity by added sucrose (50 and 100 mM) also inhibited cell proliferation. Of the hydrophobic inhibitors neither NPPB at 40 microM nor tamoxifen at 1.3 microM, added for 48 h, reduced cellular ATP; however, DIDS at 31 microM significantly reduced cellular ATP with an equivalent increase in cellular ADP. We conclude that those membrane Cl- currents that can be activated by hypotonic stress are involved in mechanisms controlling liver cell growth, and that NPPB, tamoxifen and mibefradil at their IC50 for growth do not suppress the metabolism of mouse hepatocytes.

Membrane potassium channels and human bladder tumor cells. I. Electrical properties.

These experiments were conducted to determine the membrane K+ currents and channels in human urinary bladder (HTB-9) carcinoma cells in vitro. K+ currents and channel activity were assessed by the whole-cell voltage clamp and by either inside-out or outside-out patch clamp recordings. Cell depolarization resulted in activation of a Ca(2+)-dependent outward K+ current, 0.57 +/- 0.13 nS/pF at -70 mV holding potential and 3.10 +/- 0.15 nS/pF at 30 mV holding potential. Corresponding patch clamp measurements demonstrated a Ca(2+)-activated, voltage-dependent K+ channel (KCa) of 214 +/- 3.0 pS. Scorpion venom peptides, charybdotoxin (ChTx) and iberiotoxin (IbTx), inhibited both the activated current and the KCa activity. In addition, on-cell patch recordings demonstrated an inwardly rectifying K+ channel, 21 +/- 1 pS at positive transmembrane potential (Vm) and 145 +/- 13 pS at negative Vm. Glibenclamide (50 microM), Ba2+ (1 mM) and quinine (100 microM) each inhibited the corresponding nonactivated, basal whole-cell current. Moreover, glibenclamide inhibited K+ channels in inside/out patches in a dose-dependent manner, and the IC50 = 46 microM. The identity of this K+ channel with an ATP-sensitive K+ channel (KATP) was confirmed by its inhibition with ATP (2 mM) and by its activation with diazoxide (100 microM). We conclude that plasma membranes of HTB-9 cells contain the KCa and a lower conductance K+ channel with properties consistent with a sulfonylurea receptor-linked KATP.